Leakage of fuel may take place in the combustor section of a gas turbine power plant. Leakage during engine starting may result from unburnt fuel being forced between joints which permit thermal expansion of combustor parts relative to one another. Leakage may also occur in the pipe joints which furnish fuel to the multiplicity of combustor nozzles. Fuel leakage from any source produces a risk of fire. The object of this invention is to reduce this risk.
Prior art systems of leakage fuel collection are disclosed in U.S. Pat. Nos. 3,556,444, 2,949,736 and 2,814,931. U.S. Pat. No. 3,556,444 to Kopp deals with means for handling leakage fluids in vertical takeoff and short takeoff aircraft wherein the entire engine is rotated to provide lift during landing and liftoff. Because of this change in engine attitude with respect to the gravity vector, Kopp was faced with finding a way to prevent the discharge of combustible fluids from the aft end of an engine during landing and takeoff. In U.S. Pat. No. 2,949,736, Rubbra discloses means for collecting the leakage fuel in a small sump positioned on the underside of the engine. Leakage fluids drain into the sump from between two rings used to provide a pressure seal for a thermal expansion joint in the compressor. Fuel collected in the sump is sucked into the jet pipe by a venturi pump unit which functions at engine speeds below rated rpm.
Johnson in U.S. Pat. No. 2,814,931 discloses means for collecting leakage fuels in a small tank located underneath the combustor section of an engine. The tank is supplied by a drain system which collects combustible fluids from such things as the valves, pumps and oil coolers associated with an engine. Believing it undesirable to purge the contents of the collector tank overboard, Johnson injects the leakage fluids into the stream of exhaust gas at a location just downstream of the combustor. A venturi pump is used, the pump unit being arranged to deliver the contents of the collector tank only during normal operation of the engine. During engine start up and shut down, valves act to close the outlet passage.
The three above identified patents disclose solutions for fuel leakage problems in jet turbine engines. My problem has different constraints in that my invention is pertinent to a fan-jet or turbofan engine. The turbofan engine includes a turboshaft engine which serves as a core engine to produce the power to drive the fan. In a suitable fan engine configuration the core engine is in the center of the fan airflow which is confined in an annular duct which must be streamlined to reduce aerodynamic losses. The inner wall of the annular fan duct also serves as a close-fitting shell or cowl around the core engine. Fuel leakage from the core engine and the associated piping will thus be within the confines of the cowl and must be disposed of in a manner to preclude its ignition within the cowl.